robzilla - 10:14 am on May 11, 2009 (gmt 0)
i guess we can conclude that it is a good practice to buy some expired domains instead of registering new one and develop that domain
I think you've missed the point. Generally, when a domain has expired and is registered again, Google believes that the new owner should start from scratch, so they reset all ranking factors, like PageRank. This thread, however, shows that, manually or algorithmically, they are able to make a distinction between unintentionally and intentionally expired domains.